1. Field of the Invention
The present invention relates to a method at a data and telecommunications system for transmission of data streams between a receiving terminal and a transmitting terminal via at least one fixed network including just any to number of nodes and another network consisting of links with large variation in bandwidth and quality, at which a resource reservation protocol reserves resources in said fixed network for said data streams.
2. Background Art
A computer transmits data over a network to a receiving computer. At hierarchical coding, a data stream (with real time requirements, i.e. demands on controlled delay) is divided into separate data streams with different priorities. The data streams have different demands on quality. By a resource reservation protocol, resources then are reserved in the network for the data streams. Separate reservations are made for each data stream in all nodes from the receiver to the transmitter. At hierarchical coding, the node shunts data streams according to a predefined priority as the transmission capacity of the node, has decreased. Since the data streams have real time demands, data will not be buffered.
When hierarchical coding is used over a radio channel with large variation in bandwidth and quality, the number of data streams which can be transmitted over the radio channel will vary rapidly. The radio channel is the transmission link which in most cases will set a limit to the number of data streams that can be transmitted to the receiver. The data streams that are stopped at the node closest to the radio channel are still transmitted in the fixed network and therefore load the fixed network without due cause. At the same time, the receiver wants to keep its reservations in the network during the time when some data streams are stopped, because the reservation may not be possible to be retrieved if it is deleted. For unicast traffic, i.e. one receiver of data streams and separate resource reservations for each receiver, it is possible to signal to the transmitter to stop the transmission of a data stream. For multicast traffic, i.e. a plurality of receivers of the same data streams, resources are reserved in nodes with data streams in common. Thus, the transmitter cannot stop the transmission of any particular data stream since all other receivers then should be affected.
The aim of the present invention consequently is to solve this problem and provide multicast traffic without loading the fixed network without due cause.
This aim is achieved by a method of transmitting data streams between a receiving terminal and a transmitting terminal via at least one fixed network including any number of nodes and via another network consisting of links with a large variation in bandwidth and quality. The invention includes a resource reservation protocol that reserves resources in said fixed network for said data streams. The protocol includes monitoring if the transmission capacity of a node decreases and falls below the quality requirements of a specific data stream. If so, the specific data stream is shunted, , whereupon said node transmits a message which is executed in all nodes in said fixed network so that resource reservations are then provided to said transmitting terminal for other subscribers. The message results in the networks:
updating said resource reservation for said specific data stream;
utilizing said resource reservation temporarily for other traffic;
shunting said specific data stream until further notice.
The invention shows a plurality of advantages in comparison with known technology. For instance, the fixed network will, with this resource optimization function, have a considerable capacity improvement since the network will not be loaded by data which in any case is shunted at the downstream node lacking capacity.
The receiver will not lose its resource reservations during the time a data stream is stopped, which can happen if the receiver has to make new resource reservations each time the number of data streams is changed.
Resources which in other cases would not be utilized during the time a data stream is momentarily stopped, now can be utilized.
With multicast traffic, data will be shunted in a node as close to the transmitter as possible, without other receivers of the multicast traffic being affected. Further characteristics of the present invention are given in the sub-claims.